Plants are the air-purifiers for planet earth. They clean it, and in doing so produce the oxygen we, and all animals need to survive. This happens through one of the most amazing chemical reactions you can imagine, photosynthesis. More on this a bit further down, but as a lead in to the story we'll ask a question whose answer may astound you... Imagine the largest tree you've ever seen (even in a picture) - where does the matter come from that forms the mass of wood, branches and leaves?

The earth itself is a "closed system" in that it produces everything it needs to ensure the survival and development of its inhabitants. Within the system there is a delicate balance that must be maintained. In the page below we will explore one relationship within that balance, the air-purifying plants, man and Carbon Dioxide (CO₂). We'll do so looking at things most of us use everyday as examples of mans part in this relationship (as a producer of CO₂).

At present there is much debate about people's impact on the planet. This debate is most pronounced in the discussions around global warming and our responsibility for the continued increase in CO₂ and other "greenhouse gases" released into, and consolidating in, the earth's atmosphere. Tying in directly to this problem are topics such as deforestation and the 1994 Kyoto protocols.

When you look around, it's a bit hard to comprehend we are really the newcomers on the planet. We've built so much and seem to be expanding everywhere. With our building and expansion, we use ever more fossil fuel to run our homes, our cars and the planes we fly in. Burning these fuels creates CO₂ as one byproduct of the process. Even the batteries that run our cell phones, Ipods and other gadgets use electricity for charging, which in most instances creates more CO₂.

As it turns out, CO₂ is also a very important gas in the life processes. Plants use CO₂ in the chemical process mentioned above, photosynthesis.

Photosynthesis is an extremely complex process. In its simplest form, this important reaction convert CO₂ [carbon dioxide] and H₂O [water] plus energy [sunlight] into O₂ [oxygen] and (C₆H₁₂O₆) [glucose]. The oxygen goes into the air you breathe.

6CO₂ + 6H₂O (+ light energy) -->-->-->--> C₆H₁₂O₆ + 6O₂
six molecules of carbon dioxide plus six molecules of water produce one molecule of glucose plus six molecules of oxygen

Taking the chemistry a bit further, we note that water supplies the oxygen atoms (indicated below as O^.) required for the formation of molecular oxygen. We now write the equation as: 6CO₂ + 12H₂O^. (+ light energy) -->-->-->--> C₆H₁₂O₆ + 6O₂^. + 6H₂O

And a wee bit further, photosynthesis produces carbohydrates other than glucose - cellulose and starch. They can be represented by (C₆H₁₀O₅)n.

A better representation of our equation becomes 6nCO₂ + 12nH₂O^. (+ light energy) -->-->-->--> (C₆H₁₂O₆)_n + 6nO₂^. + 7nH₂O

Why is this important you ask? Cellulose (C₆H₁₀O₅)n is a long-chain polymeric polysaccharide carbohydrate, of beta-glucose. What in the world is that you say... This forms the primary structural component of green plants. The green plants primary cell wall is made largely of cellulose and the secondary wall contains cellulose with variable amounts of lignin. Lignin and cellulose, considered together, are termed lignocellulose, which, in the form of wood, is the most common biopolymer on Earth. Now, once again, where does the matter come from that forms the mass of wood, branches and leaves?

Trees store carbon, sequestered from the air, as the wood and plant material that makes up their mass.

OK, so plants (most) use carbon in as a part of their life processes... Knowing this, how much CO₂ is sequestered by an average tree? Well, it very much depends on type of tree. For our example we'll use a mature pine tree (Pinus radiata). An acre of pine trees (~120 trees) has the potential to sequester roughly 5 tons of CO₂ per year.

Let's look at part of your "carbon imprint", your home, and make an estimate for the CO₂ it might be producing each year. To do this estimate we'll make a few assumptions. Let's say your house is about 2,000 square feet, you have a heater, an air conditioner and a water heater. Check the boxes below for the items that fit your family situation.

Think about this problem for a moment. This problem is one small component in a much larger issue. Trees have a limited life span and also create CO₂ when the die and decay or are burned in a fire. And where do the aquatic plants fit in? Did you know the ocean plants are estimated to take in as much or more CO₂ each year than the land plants? It is thought that CO₂ sequestered in plants on the oceans surface that die and descend to oceans depths may be released back into the atmosphere over a much longer timeframe than that stored in trees. Have you ever consider this as a reason for keeping the oceans clean and ensuring a thriving environment for plants? How important is this?

Interesting "Plant Talking Point" isn't it. How far can you stretch the point? We'd love to hear your thoughts on the subject and share them with others. If you'd like, please send your class discussion to: PlantingScience@botany.org. Remember, solutions are all around us. Talking about and considering options helps us develop and build on new ideas. No matter how hard it seems, think long term. What kind of world do you want for your grandchildren’s children?

Thanks for stopping by!!

The information contained in this "Plant Talking Point" was supplied by Bill Dahl of the BSA Staff Team.